linkPopover is not taken when using a Theme.

[cbazza]

Checklist

• [x] This is not covered in the repository examples.
• [x] I am using the package latest version.
• [x] This is a bug report or an enhancement proposal.

Description

Try adding a custom linkPopover on the current sample: https://github.com/niuware/mui-rte/blob/master/examples/theme/index.tsx

Object.assign(defaultTheme, {
    overrides: {
        MUIRichTextEditor: {
            root: {
                backgroundColor: "#ebebeb",
            },
            container: {
                display: "flex",
                flexDirection: "column-reverse"
            },
            editor: {
                backgroundColor: "#ebebeb",
                padding: "20px",
                height: "200px",
                maxHeight: "200px",
                overflow: "auto"
            },
            toolbar: {
                borderTop: "1px solid gray",
                backgroundColor: "#ebebeb"
            },
            placeHolder: {
                backgroundColor: "#ebebeb",
                paddingLeft: 20,
                width: "inherit",
                position: "absolute",
                top: "20px"
            },
            anchorLink: {
                color: "#333333",
                textDecoration: "underline"
            },
///////
           linkPopover: {
               padding: '32px',
           },
///////
        }
    }
})